Angiopoietin-like 3 in lipoprotein metabolism
Triglycerides and cholesterol circulate in the bloodstream as part of various lipoprotein particles. Three members of the angiopoietin-like (ANGPTL) protein family — ANGPTL3, ANGPTL4 and ANGPTL8 — have emerged as important regulators of plasma lipoprotein levels by inhibiting the enzyme lipoprotein lipase. Here, I review the role of ANGPTL3 in lipoprotein metabolism. In contrast to ANGPTL4 and ANGPTL8, ANGPTL3 is exclusively produced in the liver and can therefore be classified as a true hepatokine. ANGPTL3 cooperates with ANGPTL8 to inhibit lipoprotein lipase and is mostly active after feeding, whereas ANGPTL4 is mostly active after fasting. Inactivation of ANGPTL3 in mice reduces plasma triglyceride and free fatty acid levels and suppresses atherosclerosis. In humans, homozygous loss-of-function mutations in ANGPTL3 lead to low plasma levels of low-density lipoproteins, high-density lipoproteins and triglycerides, a condition referred to as familial combined hypolipidaemia. Heterozygous carriers of loss-of-function mutations in ANGPTL3 have a lower risk of coronary artery disease than non-carriers. At present, researchers are investigating antisense oligonucleotide and monoclonal antibody-based inactivation of ANGPTL3 in human clinical trials for the therapeutic management of dyslipidaemia and atherosclerosis. Thus, ANGPTL3 is an important liver-derived regulator of lipoprotein metabolism that holds considerable promise as a target for atherosclerosis.